In the extraction of raw materials in mining it is necessary for example to separate out the desired reusable material particles from the extracted rock. Reusable material in ore extraction are frequently particles of magnetic or magnetizable material which are already contained in the ore and/or particle agglomerates, which arise from non-magnetic valuable minerals and additional magnetic or magnetizable auxiliary particles added to them.
“First particles of magnetic or magnetizable material” are to be understood below not only as particles of the magnetic or magnetizable material already contained in ore but also such magnetically separate particle agglomerates comprising auxiliary particles.
The reusable material particles or agglomerates including the reusable material particles are to be separated from non-valuable particles of non-magnetic or non-magnetizable material.
A mineral or mineral deposit containing metal more or less coalesced with a slag is referred to as an ore. The term “slag” refers to accompanying material which occurs together with the ore minerals, such as quartz, calcite, dolomite etc. Particles of magnetic or magnetizable material already contained in the ore, such as copper, iron etc. are as a rule bound to non-magnetic or non-magnetizable particles of slag and are to be separated from said particles.
The ore is generally crushed and conveyed to a device which promotes the separation of the reusable material particles. To this end the crushed ore is mostly fluidized. The fluid formed involves either a suspension in which the ore particles are dispersed in a fluid or an aerosol in which the ore particles are dispersed in a gas. Suspensions, as are typically created in mining during the extraction of ores for instance, are also referred to as sludges.
In already known methods of magnet separation or magnetic separation use is made of the fact that, in a suitable magnetic field arrangement or magnetic induction arrangement, the magnetic or magnetizable particle experiences a force which moves it or holds it still against other forces acting on it. Such forces are for example gravity or hydrodynamic friction forces in a flowing liquid medium. The magnetic force acting in a magnetic induction B on a magnetic or magnetizable particle is proportional to a product of the magnetic induction B and the component of the gradient of the magnetic induction B in the direction of the magnetic induction B.
To enable a separation of the particles which is as effective as possible to be carried out, fluids in the form of suspensions are chemically pretreated. This is especially to be understood as treating non-magnetic reusable material particles of ore such that they bind themselves to magnetic or non-magnetic auxiliary particles added thereto, such as magnetite for example, and can be magnetically separated together with these. For this purpose the surface of the non-magnetic reusable material particle is selectively functionalized, with sulfidic ores for instance with the aid of suitable xanthates. If the added magnetic or magnetizable auxiliary particles are also functionalized in a similar manner, these functional layers can enter into stable compounds with one another and thus lead to the formation of stable particle agglomerates of magnetic or magnetizable auxiliary particles and non-magnetizable reusable material particles. These agglomerates can then be separated from the suspension as magnetizable individual particles.
At present both permanent magnets and also electric magnets are used in magnetic separators.
Permanent magnets are to be found for example in the widely-used drum separators where, circulating in the drum, they act on magnetic or magnetizable particles.
DE 31 20 718 C1 discloses a further drum magnet separator for separating and sorting magnetizable substances from a mixture containing magnetizable and non-magnetizable substances, wherein the magnet system of the magnet separator generates a traveling field.
A use of electromagnets is especially known from what is referred to as high-gradient magnetic separation, in which magnetizable structures, such as needles or cutting edges, form a grid in an electrically-generated often initially homogeneous magnetic induction B. The grid structure generates a locally strongly inhomogeneous magnetic induction B with marked gradients.
DE 32 47 557 A1 describes a device for high-gradient magnetic separation of the finest magnetizable particles from a flowing medium.
A disadvantage of such high-gradient magnetic separators is that, often to remove the separated magnetic or magnetizable particles, the magnetic induction B is switched off and a back flushing process has to be carried out. This means that continuous operation is not possible.
In the interim it has also proved disadvantageous for the operation of devices for magnetic separation if the permanent magnets or electromagnets generating the magnetic induction B during the separation process have to be mechanically moved, since these types of devices are susceptible to faults.
U.S. Pat. No. 6,120,735 describes a method and device for fraction sorting of cells comprising a two or four-pole magnet arrangement.
U.S. Pat. No. 4,961,841 describes a device and a method for separating particles in a gravitation field based on separation into their magnetic properties and their density.
U.S. Pat. No. 5,169,006 describes a continuous magnetic separator comprising rods with alternating areas of non-magnetic and ferromagnetic material.